1. Field of the Invention
The present invention relates to an electromagnetic valve and, more particularly, to a pressure-balanced electromagnetic valve suited for controlling the flow of pressurized gases.
2. Description of the Prior Art
The technology of using a disc-type electromagnetic valve as means for controlling the supply of a liquid such as a liquid fuel is well known in the art, as is disclosed in U.S. Pat. Nos. 4,643,222, 4,673,163, 4,677,327, 4,678,000, 4,765,302 and so on. In these prior arts, a plate-shaped stator and an armature are arranged to face each other in a housing, and there is fixed at the center of the armature a valve rod which extends through the housing to an outside valve body as far as it faces a fluid inlet/outlet passage formed in the valve body. When coils arranged in the stator are energized, the stator is magnetized to attract the armature so that the valve rod may be moved in the direction to open or close the valve.
Another disc type electromagnetic valve is known in Japanese Patent Laid-Open No. 120017/1978. This prior art is different from the foregoing one in that the liquid inlet/outlet and the passage are formed in one casing. Specifically, a confined block is fixed in the opening of the casing accommodating a stator, and a passage chamber is formed between the block and the stator and equipped with fluid inlet and outlet which are out of shift from each other by 90 degrees. Moreover, an armature is arranged as a valve member in the passage chamber and is attracted by energizing a coils, which are arranged in the stator, so that it is moved apart from the surface of the confined block to provide the communication between the inlet and the outlet.
In either of the prior arts, the coils are provided in plurality such that they are mounted in a plurality of endless grooves formed in the stator and such that their adjacent ones are energized in opposite directions. As a result, magnetic fluxes of different directions are generated between the stator and the armature so that the armature can be actuated at a high speed.
In either of the prior arts, moreover, the armature is urged apart from the coil-arranged surface of the stator by the action of the spring which is interposed between itself and the housing (or casing). In the normal closed electromagnetic valve, more specifically, the spring is used as an element for blocking the passage when the stator is deenergized. In the normal open type, on the other hand, the spring is used as an element for opening the passage.
From the aforementioned characteristics, however, the electromagnetic valve of this kind frequently has its power supply circuit built the electronic control system and subjected to a duty ratio control. It is, therefore, desirable for the electromagnetic valve to have a stable operation and a quick responsiveness. For this desire, it is appropriate that the force of the aforementioned spring be set at a weak level. In case the fluid is an incompressible one such as oil, there arises no serious problem. In the case of high compressible gases represented natural gases or compressed air, on the contrary, the pressure is liable to fluctuate due to their characteristics to cause pulsations. As a result, the spring is compressed by the pulsations of the fluid flowing from the inlet to the passage in case the armature is pressed by a weak force. This causes the normal closed type to allow the armature to leave the valve seat accidentally thereby to open the passage and the normal open type to close the passage. In order to avoid such unstable operations, the practical answers to the problems are nothing but to set the spring force at a high level by predicting the pressure fluctuations of the fluid. However, the strengthening of the spring is to increase excess loads. As a result, the armature has to be attracted against the strengthened spring force so that the sensitivity of opening or closing the valve never fails to be deteriorated.